The present invention relates generally to dust caps that are mounted upon ferrules to protect the front faces of the ferrules from contaminants and, more particularly, relates to translucent dust caps and an associated method for testing the continuity of an optical fiber jumper that has translucent dust caps mounted upon the opposed ends thereof.
Once a fiber optic connector has been mounted upon the end portion of an optical fiber and the front face of the ferrule of the fiber optic connector has been polished, a dust cap is commonly mounted upon the ferrule. The dust cap protects the polished front face of the ferrule from contaminants or other debris that would otherwise degrade the performance of the resulting optical system. For example, fiber optic connectors are generally mounted upon the opposed ends of an optical fiber jumper during the manufacturing process. In order to protect the front faces of the ferrules of the fiber optic connectors from contaminants and other debris following the polishing of the front faces of the ferrules, dust caps are typically mounted upon the ferrules prior to packaging and shipping the optical fiber jumper.
Conventional dust caps are fabricated from an opaque plastic material, such as a low density polyethylene material. This material is advantageous in that it is relatively inexpensive. Unfortunately, conventional dust caps tend to bleed off a plasticizer that can be transferred to and contaminate the front face of the ferrule. A conventional dust cap includes a sleeve that defines a bore extending lengthwise between opposed first and second ends. The first end of a conventional dust cap is open to permit the ferrule to be inserted into the bore. In contrast, the second end of the dust cap is closed. A conventional dust cap is generally designed to be mounted upon a ferrule by inserting the front face of the ferrule through the open first end of the dust cap and into the bore and thereafter slideably advancing the dust cap upon the ferrule. The slideable advancement of the dust cap typically continues until the first end of the dust cap contacts an inwardly extending flange of the inner housing of the fiber optic connector. A conventional dust cap therefore defines a straight bore having a constant diameter that equals or slightly exceeds the diameter of the ferrule and that is slightly longer than the length of the ferrule that is anticipated to be inserted into the dust cap. As such, the front face of the ferrule does not generally contact the closed second end of the dust cap and thereby avoids picking up contaminants or other debris carried by the second end of the dust cap.
A dust cap is typically molded about a pin that defines the bore. Upon pulling the pin out of the dust cap following the molding process, flakes of material may be pulled outwardly from the second end of the dust cap so as to extend into the bore. In some instances, these flakes of material contact the front face of the ferrule once the dust cap is mounted thereupon. In instances in which flakes of material from the second end of the dust cap do contact the front face of the ferrule, contaminants or other debris can be transferred to the front face of the ferrule even though the front face of the ferrule is otherwise spaced slightly from the second end of the dust cap.
In order to facilitate the mounting of a dust cap upon a ferrule, a conventional dust cap also typically defines a groove that opens into the bore and that extends lengthwise from the first end of the dust cap through the entire bore. As will be apparent, the groove facilitates the mounting of a dust cap upon a ferrule by permitting air that would otherwise be trapped within the bore between the front face of the ferrule and the second end of the dust cap to escape. Since the groove runs the length of the bore, however, contaminants and other debris can also enter the bore via the groove even after the dust cap has been fully mounted upon the ferrule. These contaminants and other debris that enter via the groove may disadvantageously be deposited upon the front face of the ferrule.
The removal of the dust cap from a ferrule will obviously expose the front face of the ferrule to contaminants and other debris. Moreover, the removal of the dust cap from the ferrule will also electrically charge the ferrule such that contaminants and other debris are electrically attracted to the ferrule. As such, it is desirable for the dust cap to remain on the ferrule from immediately following the polishing of the front face of the ferrule to some time immediately preceding the interconnection of the fiber optic connector during installation of the optical fiber. Unfortunately, a dust cap must typically be removed at least once after its initial mounting upon the ferrule following the polishing of the front face of the ferrule and prior to its ultimate removal from the ferrule in the course of installing the optical fiber.
For example, during a conventional manufacturing process in which fiber optic connectors are mounted upon the end portions of one or more optical fibers, such as during the fabrication of optical fiber jumpers, the front face of the ferrule is typically polished and the optical fiber jumper is then subjected to performance tests, including tests that measure the insertion loss and the back reflection prior to mounting a dust cap upon the ferrule. After mounting the dust cap upon the ferrule, an outer shroud is assembled to the inner housing and a boot is inserted into the rear of the outer shroud in order to complete the assembly of the fiber optic connector.
Even though performance tests were conducted following the polishing of the front faces of the ferrules, optical fiber jumpers must generally be tested again for optical continuity immediately prior to being packaged and shipped to a customer in order to minimize the number of defective optical fiber jumpers that are delivered. In this regard, a continuity test is generally desirable since the assembly of the outer shroud and the boot following the prior performance testing and the mounting of the dust cap upon the ferrule could have broken an optical fiber or otherwise impaired the continuity of the optical fiber jumper. The opaque dust caps must therefore be removed from both ends of the optical fiber jumper to permit the continuity of the optical fiber jumper to be tested. If the optical fiber jumper passes the continuity test, the dust caps are then remounted upon the respective ferrules prior to packaging and shipping the optical fiber jumper to a customer. During the relatively brief time in which the dust caps are removed from the respective ferrules, however, contaminants and other debris may be deposited upon the front faces of the ferrules, especially in light of the electrical charge that may be imparted to the ferrules upon removing the dust caps therefrom. Thus, the resulting system performance may be degraded once the optical fiber jumper is installed due to the contaminants and other debris that are deposited upon the front faces of the ferrules.
A dust cap is therefore provided that addresses these and other shortcomings of conventional dust caps in order to further reduce the opportunity for contaminants and other debris to be deposited upon the polished front face of a ferrule. The dust cap can be constructed such that at least the closed end is translucent in order to permit optical communication with an optical fiber upon which the ferrule is mounted while the dust cap remains mounted upon the ferrule, such as during continuity testing. The dust cap can also include an internal chamfer that extends radially inward for engaging the ferrule in order to insure that the front face of the ferrule is adequately spaced from the closed end of the dust cap, thereby preventing the transfer of contaminants or other debris from the closed end of the dust cap to the polished front face of the ferrule. In addition, a dust cap can define a groove that is designed to vent air during the mounting of the dust cap upon a ferrule, but that extends only to a medial portion of the dust cap in order to prevent contaminants or other debris from passing through the groove and being deposited upon the front face of the ferrule once the dust cap has been fully mounted upon the ferrule. A method for checking the continuity of an optical fiber jumper is also provided in which the translucent dust caps remain mounted upon the respective ferrules while light is introduced into one end of the optical fiber jumper and light is emitted from and monitored at the other end of the optical fiber jumper. Accordingly, the dust cap of the present invention advantageously permits the continuity of an optical fiber jumper or other types of optical fibers to be confirmed without having to remove the dust caps from the respective ferrules that would subject the front faces of the ferrules to contaminants or other debris and subsequently impair the system performance once the optical fiber jumper was installed.
The dust cap includes a sleeve extending lengthwise between opposed first and second ends. The sleeve defines a lengthwise extending bore that opens through the first end for receiving at least a portion of the ferrule. The dust cap also includes an end member for closing the second end of the sleeve. In one advantageous embodiment, at least the end member is translucent for permitting optical communication with the optical fiber upon which the ferrule is mounted while the dust cap remains mounted upon the ferrule. Typically, the sleeve and the end member are integral such that the sleeve is also translucent. For example, both the sleeve and the end member can be formed of nylon. According to this embodiment, the end member can also include a lens. For example, the lens can include an outer planoconvex lens proximate the outer surface of the end member. Additionally, the lens can include an inner lens proximate the inner surface of the end member. In either instance, the lens serves to focus incident optical signals upon the optical fiber upon which the ferrule is mounted and to expand optical signals emitted by the optical fiber in order to facilitate optical communication therewith.
In one embodiment, a medial portion of the sleeve defines an internal chamfer that extends radially inward for engaging the ferrule such that the front face of the ferrule is spaced from the second end of the sleeve. Thus, contaminants and other debris will not be transferred from the closed second end of the sleeve to the polished front face of the ferrule. In this embodiment, the portion of the bore extending between the first end of the sleeve and the internal chamfer generally has a larger diameter than the portion of the bore extending between the internal chamfer and the second end of the sleeve.
The dust cap of one embodiment of the present invention also defines a groove opening into the bore and extending lengthwise through only a portion of the sleeve. In this regard, the sleeve defines the groove to extend only from the first end of the sleeve to a medial portion of the sleeve. Preferably, the medial portion of the sleeve to which the groove extends is selected such that the front face of the ferrule will be positioned between the medial portion of the sleeve and the second end of the sleeve. In one embodiment, for example, the sleeve defines the groove to extend only from the first end of the sleeve to the medial portion of the sleeve that defines the internal chamfer. Thus, even though the groove permits air to vent from the bore while the dust cap is being mounted upon the ferrule, the front face of the ferrule will be isolated from the groove and, in turn, from the external environment once the dust cap has been fully mounted upon the ferrule, thereby protecting the polished front face of the ferrule from contaminants and other debris that may enter the groove.
A method is also provided according to one embodiment of the present invention for testing the continuity of an optical fiber jumper. In this regard, the optical fiber jumper includes at least one optical fiber, first and second fiber optic connectors including respective ferrules mounted upon opposed ends of the at least one optical fiber and at least one dust cap having a translucent end member mounted upon a respective ferrule. According to this method, light is introduced into one end of the optical fiber and the light emitted by the other end of the at least one optical fiber is monitored to test the continuity of the optical fiber jumper while the at least one dust cap remains mounted upon the respective ferrule. More commonly, the optical fiber jumper includes first and second dust caps with translucent end members mounted upon the ferrules of the first and second fiber optic connectors, respectively. In one advantageous embodiment, the end member of each dust cap includes a lens such that introducing light into one end of the least one optical fiber also includes focusing light into one end of the at least one optical fiber. Conversely, monitoring the emitted light also includes expanding the light emitted by the other end of the at least one optical fiber. As such, the continuity of an optical fiber jumper can be checked without having to remove the dust caps from the respective ferrules that would disadvantageously expose the polished front faces of the ferrules to contaminants and other debris. By providing a dust cap and an associated method for testing the continuity of an optical fiber jumper without having to remove the dust caps, the resulting performance of the optical fiber jumper should be improved since the polished front faces of the ferrules will generally have fewer contaminants and other debris than conventional ferrules.